The invention falls notably in the field of microwave microelectronic packaging, in particular for producing microwave packages comprising an integrated and moisture-resistant shielding. These packages are for example used in complex microwave equipment items such as airborne electronic scanning radars. More generally, the field of application is that of the narrow band or wide band microwave equipment items, the packages being able to be used in all high-frequency applications, even those with high signal integrity specifications.
The only microwave packaging technologies that are moisture resistant rely on the use of inorganic materials or on the encapsulation of the components using injected organic resins. The inorganic solutions notably use metallic hermetic packages with glass beads for the inputs/outputs or ceramics.
The solutions that use inorganic materials present a number of drawbacks. These results are notably:                packages that are expensive and heavy, because of the materials used, metal or ceramic;        bulky solutions, notably using packages with internal cavities, very often with peripheral interconnections;        solutions for which the reliability of mounting, in the equipment item concerned, is generally problematic, because of differences in expansion coefficient with the printed circuits on which they are assembled.        
In the case of injected organic packagings, the end result is objects which are intrinsically unshielded electrically and which cannot therefore be used as such in complex equipment items where crosstalk is a critical parameter. The package usually encountered is the so-called QFN (Quad Flat No-Lead) package which has generally peripheral inputs and outputs.
There is a need for compact packages that meet the following constraints:                protecting the encapsulated functions from moisture, notably to take account of all the MMIC (Microwave Monolithic Integrated Circuit) technologies;        obtain a good mounting reliability;        maintain the possibility of changing the packages on the board;        being suitable for dissipating heat;        having a capacity to be able to do 3D, that is to say, according to the architectures, even with ultra-compact packages, stacking microwave functions according to the integration density of the chips used.        
The microwave applications require the use of III-V semiconductors with high charge mobility. These components operate in analogue mode and are therefore very sensitive to the quality of the interconnections that they use and to the interferences that they can encounter. In addition, since they operate at significant voltages and currents, the electronic components (transistors, capacitors, resistors, etc.) can be subject to corrosion phenomena when the latter are operating, for example electrochemical corrosions through Nernst potential difference.
To avoid any problem of reliability, the manufacturers have first of all developed hermetic packages that use inorganic materials (metals or ceramics as indicated previously) which are heavy and bulky. In order to reduce the weight, the volume and the cost of manufacturing of the microwave packagings, plastic packages have begun to be developed with a loss of electromagnetic performance levels that is significant but acceptable for the narrow band applications such as mobile telephony.
The field of electronic packaging has been the subject of numerous developments. The package of BGA (Ball Grid Array) type with surface interconnections was developed in response to the QFP (Quad Flat Pack) technology with peripheral interconnections in order to increase the interconnection density. This type of BGA package has experienced high growth for silicon semiconductor-based digital applications.
In the field of microwave organic packagings, many solutions have also been developed. Solutions that can be cited include the CSP (Chip Scale Package) technology for narrow band applications with an operational frequency below 2.17 GHz. Plastic packages capable of managing heat dissipations of the order of 60 W to 100 W have also been developed for applications ranging up to 2.17 GHz. There are plastic packages for high-frequency applications, up to 35 GHz, in narrow band of QFN type. Plastic packages of QFN or TSOP (Thin Small Outline Package) type operate up to 12 GHz. A package with cavity using a thermoplastic material called LCP (Liquid Crystal Polymer) was developed at the end of the last decade for high-frequency applications. During the same period, the concept of packaging for microwave applications in LTCC (Low Temperature Cofired Ceramic) technology and in LCP organic materials, has emerged. The package of QFP (Quad Flat Pack) type, with cavity, has allowed encapsulation with satisfactory performance levels, of a wide band function.
Moreover, patent applications FR 2 849 346 and FR 2 877 537 describe a BGA organic packaging technology with cavity.
As has been indicated previously, the only moisture-resistant microwave packaging technologies that are compatible with all the MMICs rely on the use of inorganic materials (metal packages with glass beads for the inputs and outputs or ceramic packages), or on the encapsulation of the components using injected organic resins. The solutions based on inorganic materials lead to the use of expensive and heavy packages, and are bulky, particularly because of the internal cavities and the peripheral interconnections. The solutions based on organic materials have the major drawback of not being electrically shielded, and cannot therefore be used in complex equipment items where cross talk is a critical parameter without additional partitioning.